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Cover Story Toward tougher trellises


Recommended design changes are aimed atmaking orchard support systemsmore able to withstand high winds and heavier loads.


By Judie Steeves W


ith today’s higher-density methods of growing fruit, coupled with more-extreme weather events, including high wind gusts, support system designs for those plants must be updated, says Dwayne Tannant, engineering professor at UBC-O.


Today’s methods are 30 years old, and in need of replacement. Like the systems themselves, a new design for those trellis systems is overdue, he reported to a group of agrologists this spring.


In a project funded by the Ministry of Agriculture and led by agrologist Keith Duhaime, with Tannant and a number of his engineering students, the old manual on Support Systems for High Density Orchards has just been updated, and it’s now available under Replant Program on the B.C. Fruit Growers Association website at www.bcfga.com


Dwayne Tannant particularly high winds.


For instance, in September, 2015, some Kelowna growers’ orchards were buffeted by winds that gusted to 54 kilometres per hour, while high winds in the Penticton area were recorded up to 53 kph in October of 2017 and in the Creston area, winds of 39 kph were recorded in August of 2014. Over time, he says, winds weaken the posts and the structures.


In that 2015 storm in the Okanagan, some growers lost not only crops, but whole rows of trees were pushed over as the gusts damaged the support system they relied on.


After conducting research into existing trellis systems, some of which have failed growers in the past few years, Tannant created the 2018 revision to the existing design of trellises which he feels should last for 20 years into the future without failing. “The old support systems were set up for lower loads,” explains Tannant, noting that the difficulty usually occurs in late summer or early fall when the weight of both the fruit and the foliage is at its maximum and a gusty storm blows in accompanied by


Trellis design from revamped support systems manual recommending 12-foot pressure-treated posts that are at least four inches in diameter.


In today’s high-density plantings, dwarf rootstocks are used to grow a spindle-type tree so fruit is produced faster and crop loads are heavier, improving growers’ returns and the speed with which a crop can be harvested after replanting. However, these new trees have a limited branch network so there’s inadequate support by the tree for the crop, making it necessary for a support system to be installed. Although such infrastructure is more expensive initially, they are more efficient and profitable over the their production life because the tree is encouraged to put its energy into production of fruit rather than wood.


As well, the trellis is a uniform structure for training the tree British Columbia FRUIT GROWER • Summer 2018 7


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